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Abstract

LES ARTHROPODES ECTOPARASITES DE VERTÉBRÉS AU CANADA

Résumé

Les arthropodes ectoparasites sont des éléments divers de la faune canadienne et affectent fréquemment la performance et le bien-être de l'homme, des animaux domestiques et des animaux sauvages. La faune n'est pas bien connue, avec 17% seulement des espèces anticipées, décrites. Les acariens et les poux broyeurs en particulier, demandent plus d'étude. Le potentiel d'enquête scientifique des relations écologiques, physiologiques et systématiques des ectoparasites et de leurs hôtes est considérable. Malheureusement, il n'y a eu aucune recherche coordinée, et une grande partie de la recherche a été dirigée vers des espèces économiquement importantes ou vers des porteurs de maladies.  Par conséquent, une vue relativement préjugée des relations de la faune nous est présentée.

La Commission biologique du Canada (Arthropodes terrestres) recommande donc des méthodes pour améliorer l'état de connaissances des arthropodes ectoparasites canadiens: ressources supplémentaires visées à des objectifs long-terme, une augmentation de conscience parmis une variété de disciplines biologiques, et des possibilités fructeuses pour des recherches futures.

Introduction

Arthropod ectoparasites are a diverse and highly adapted group of animals that inhabit the external body surfaces of vertebrates. They may live permanently on their host, or they may occupy the host's nest and immediate environment, and visit the body of the host periodically. In either case, there is a close dependency on the host for various life-sustaining resources. The relationship between parasite and host is an ancient one, and the mechanisms by which parasites seek, identify and maintain contact with their host are sophisticated and complex.

The potential and need for study of ectoparasites in Canada are as diverse as the fauna itself. There is a rich vertebrate host fauna which is reasonably well known, inhabiting a range of widely different habitats and geographic regions. Some of these host species are threatened or endangered where they are currently found in Canada, and if they disappear, there is a good chance that many species of parasites will suffer the same fate. Some ectoparasites are vectors of important human and wildlife diseases (e.g. Plague, Rocky Mountain Spotted Fever, Lyme Borreliosis), or create undesirable dermal immune responses (e.g. chigger mites, scabies). Ectoparasites have the potential to affect the health and general well being of wildlife and domestic animal populations, and they may seriously restrict habitat and land resource use because of stress and reduced performance of animals living in a particular habitat. Development and use of land designated for recreational activities may also be affected by the threat of infestation of people and their companion animals by undesirable ectoparasites.

Therefore, the potential economic impact of ectoparasites is substantial. Despite this economic focus for study, research on most groups of ectoparasites has been fragmentary. This brief describes the relationships between arthropods and vertebrates, comments on the nature of the ectoparasite fauna of Canada as a whole, and indicates potential for study. Recommendations show how integrated, long-term studies on the ectoparasites in Canada can be supported.

Associations Between Vertebrates and External Arthropod Parasites

Vertebrates offer a variety of potential resources, and the nature and availability of these resources may influence the success of any ectoparasite species. The body itself is a cistern of renewable, nutrient-rich fluids. Some of the best known ectoparasites, the ticks, fleas and sucking lice among them, have modified mouthparts by which they can penetrate the skin and obtain these fluids. Specificity of the association with a vertebrate may, in part, be influenced by host behavior, the chemical nature of the body fluids, and the microhabitat created by skin and pelage.

The external surface of the body, too, is rich in potential food resources. Abraded and sloughed skin, sebaceous secretions, and microbial growth are consumed by some arthropods, for example the Mallophaga. The vertebrate body is a myriad of microhabitats in which scavenging species can be found. There are folds, pockets, and invaginations of the skin, and outgrowths of feathers or hair. All, in combination with variations over different regions of the body, allow for a high degree of specificity and relative isolation. Consequently, a single animal may harbour several ectoparasite species, some of which appear to compete actively with one another for available resources.

Typically, vertebrates select specific habitats in which to live, and may variously modify those habitats to suit their needs. Survival of some arthropods may be affected by biotic and abiotic factors quite independent of the host and its activity. Ixodid ticks, in particular, rely on host movement in specific areas to enhance the probability of encounter, but because they spend most of their life off the host, environmental conditions are as important to their survival as the presence of the host.

The Canadian Arthropod Ectoparasite Fauna

It is not the intent here to provide extensive analysis of the relationships among ectoparasites and their hosts. There is evidence of a long association with a particular host species or group of species, and hence there is a varying degree of  host specificity. There are several excellent reviews on the subject, the references for which are provided in Appendix 1. Nevertheless, it is useful to examine the breadth of the fauna, and treat each major group in general terms to show the extent of our knowledge on the group in Canada. Relevant data have been extracted from Danks (1979) to compile Appendix 2. 

Among the major groups of the Acari, only the ticks (Metastigmata) are reasonably well known. The ticks are a relatively small group of medical and veterinary importance, with a larger body size than most acarines, and they have been studied by some Canadian specialists over the years (e.g. J.D. Gregson, P.R. Wilkinson). Concerns about their vector potential for Rocky Mountain Spotted Fever, tularemia and more recently, Lyme Borreliosis, and the ability of some species to induce tick paralysis have provided impetus for study. The Mesostigmata, on the other hand, are poorly known, with less than 30% of the Canadian fauna described or recorded. The very small families (e.g. Spincturicidae, Ixodorhynchidae), or those with economically important species (e.g. Dermanyssidae) are the better known, while others have been neglected. Among the Laelapidae and Haemogamasidae, only some species are ectoparasites, but relationships with hosts or with the nest environment are poorly known.

The prostigmatid mites (Acariformes) are enormously diverse in their life histories and degree of association with vertebrate hosts. Unfortunately, no one in Canada has ever directed their attention to this group of ectoparasites, and less than 2% of the total fauna is recorded or described. There is tremendous potential for study, particularly on the species associated with the skin and feathers of birds.

The pentastomids are a small, curious group of species in Canada. They can only loosely be defined as ectoparasites, since the adults are found in the air sacs of birds, or the respiratory passages of reptiles and mammals. They have been rarely encountered in Canada, and warrant further investigation.

Among the six orders of insects containing ectoparasites, most have received sufficient attention that the Canadian species have been described. The Siphonaptera are perhaps the best known because of over 40 years of work invested by G.P. Holland. The Anoplura includes many species associated with humans and domestic animals, which have received some attention. The ectoparasitic flies, beetles and bugs comprise few species. They are so striking in appearance, and are such a surprise when encountered, that they are usually preserved and retained when seen. The Mallophaga, however, are desperately in need of study with less than 50% of the Canadian species known.

Potential for Study

Arthropod ectoparasites and their hosts offer unique opportunities for research. These are divided into three broad, but of course interdependent, categories below.

Resources for Study

The study of arthropod ectoparasites has been driven in the past in Canada principally by the need for answers to specific problems affecting man, domestic animals or wild game species. Our knowledge of the fleas arose from initial concerns about plague in Western Canada. Where ticks caused paralysis and death in livestock in British Columbia, a specialist in the field was appropriated to conduct the needed research. Lice, keds, and mites are frequent pests on confined livestock and poultry and several studies have been conducted to measure impact on performance and for pest control.

The number of researchers available in Canada to respond to new problems is relatively small, and many of these researchers study other pests of vertebrates as well. Consequently, there is little flexibility in the system. A good example is in the need for information on the recently derived problem of Lyme Borreliosis in Canada. Lyme Borreliosis is a tick-borne disease that can be debilitating in clinical human cases. The bacterial pathogen responsible and the tick vector, Ixodes dammini Spielman et al., might be widespread in Canada. However, it has been difficult to mobilize the available resources to obtain answers to questions being raised by health officials and the public. We would be naive to believe that Lyme Borreliosis is a unique example where relevant basic information on ectoparasites is deficient, and where new problems cannot be addressed.

Therefore, it is necessary to maintain a basic core of expertise in Canada. This expertise should not be vitally linked to economically important problems. Typically, vector-borne diseases and problems with ectoparasites in Canada have been sporadic and generally isolated in their focus. Although we must continue to address these problems, we cannot support a research program that lives or dies on the basis of the number of clinical cases per year. Such programs do not survive over the long term in this country.

Rather, we should turn to the natural heritage of Canada to form the basic structure and support for continued research. While the amphibian, reptile, bird, and mammal faunas are reasonably well known in Canada, their ectoparasites are not. In any particular region of Canada, a great deal remains to be learned about the nature of the ectoparasite fauna, the ecological relationships with the available hosts, and the physiological mechanisms related to successful growth and development. Research on ectoparasites might very profitably be linked to that being carried out by vertebrate ecologists and physiologists, as well as parasitologists studying different classes of organisms in the same hosts. Opportunities for interdisciplinary research are available and should be pursued. Such collaboration would certainly enhance the vitality of a research program, and may eventually provide essential information for successful management and survival of threatened or endangered species. In the end, all will profit by a better understanding of the fauna of Canada, and our ability to respond to critical problems in vector-borne disease epidemiology and livestock or wildlife management will be greatly increased.

Recommendations

The arthropod ectoparasites of vertebrates are not well known in Canada, despite the significance of these organisms to man, domestic animals, and wildlife. The   Biological Survey of Canada (Terrestrial Arthropods) therefore seeks to coordinate activities that will enhance research and encourage awareness. To this end, the Survey recommends:

APPENDIX 1 - SELECTED REFERENCES

Askew, R.R. 1971. Parasitic insects. Heinemann Educational, London. xvii + 316 pp.

Banfield, A.W.F. 1974. The mammals of Canada. National Museums of Canada, Toronto University  Press. xxv + 438 pp.

Cook, F.R. 1984. Introduction to Canadian amphibians and reptiles. National Museums of Canada,  Ottawa. 200 pp.

Danks, H.V. (Ed.). 1979. Canada and its insect fauna. Mem. ent. Soc. Can., No. 108. 573 pp.

Godfrey, W.E. 1986. The birds of Canada. National Museums of Canada. 595 pp.

Gregson, J.D. 1956, The Ixodoidea of Canada. Can. Dep. Agric., Publ. 930. 92 pp.

Holland, G.P. 1958. Distribution patterns of northern fleas (Siphonaptera). Proc. Xth Int. Congr. Ent. (Montreal, 1956) 1: 645-658.

---------- 1963. Faunal affinities of the fleas (Siphonaptera) of Alaska: with an annotated list of species. Tenth Pacific Science Congress Proceedings. pp. 45-63.

---------- 1985. The fleas of Canada, Alaska and Greenland (Siphonaptera). Mem. Ent. Soc. Can., No. 130. 631 pp.

Kennedy, M.J. 1986. Synopsis of the parasites of domesticated mammals of Canada. Alberta Agriculture, Animal Health Division. 53 pp.

Kennedy, M.J., and R.A. Newman. 1986. Synopsis of the parasites of vertebrates of Canada. Ectoparasites of terrestrial mammals. Alberta Agriculture, Animal Health Division. 109 pp.

Kim, K.C. (Ed). 1985. Coevolution of parasitic arthropods and mammals. John Wiley, New York. xiv + 800 pp.

------------, H.D. Pratt, and C.J. Stojanovich. 1986. The sucking lice of North America. An illustrated manual for identification. Pennsylvania State University Press, University Park. xii + 241 pp.

Marshall, A.G. 1981. The ecology of ectoparasitic insects. Academic Press, London. xvi + 459 pp.

Price, P.W. 1980. Evolutionary biology of parasites. Monographs in Population Biology, Princeton University Press, Princeton. xi + 237 pp.

Rothschild, M., and T. Clay. 1952. Fleas, lice and cuckoos: a study of bird parasites. MacMillan, New York. 305 pp.

Timm, R.M. 1983. Fahrenholz's rule and resource tracking: a study of host-parasite tracking. pp. 225 265 in: Mtecki, M.H. (Ed.), Coevolution. University of Chicago Press, Chicago.

Traub, R. 1972. The zoogeography of fleas (Siphonaptera) as supporting the theory of continental drift. J. Med. Ent. 9: 584-589.

Wheeler, T.A., and W. Threlfall. 1989. Synopsis of the parasites of vertebrates of Canada. Ectoparasites of birds. Alberta Agriculture, Animal Health Division. 85 pp

Whitaker, J.O., Jr., and N. Wilson. 1974. Host and distribution lists of mites (Acari), parasitic and phoretic, in the hair of wild animals of North America, north of Mexico. Am Midl. Nat. 91: 1 67.

Wilson, N. 1967. Ectoparasites of Canadian birds and mammals. Proc. ent. Soc. Wash. 69: 349-353.

APPENDIX 2 - SYNOPSIS OF ARTHROPOD ECTOPARASITES OF VERTEBRATES IN CANADA